The present invention relates to a blood oxygenator and to a method for oxygenating blood.
The history of safe and reliable blood oxygenators is relatively brief. Such oxygenators are used in open-heart surgery and other operations and treatments of the body when it is necessary to establish an extracorporeal circulation system for temporarily assuming the functions of the heart and lungs of the patient. In such a system, the oxygenator operates to perform the function usually performed by the lungs of the patient, i.e., the life-supporting transfer of oxygen into the blood and carbon dioxide out of the blood. The oxygenator is used in association with a pump which performs the function of the heart to cause circulation of the blood. Thus, early versions of the oxygenator were often referred to as "heart-lung" machines. The early heart-lung machines were typically rotating discs which passed through a pool of blood, but were only partially immersed therein such that the free surface of the disc exposed the blood to oxygen and accomplished some gas transfer. After this, bag-type oxygenators were introduced which were superior to the disc oxygenators, but which left much to be desired.
A major advance occurred in the mid-1960's when the rigid (or hard-shell) bubble oxygenator was developed. The history of such oxygenators had its beginnings in the device shown in Raible, et. al. U.S. Pat. No. 3,468,631 and they first came into clinical use with the development of the devices shown in Bentley, et. al. U.S. Pat. Nos. 3,488,158 and 3,578,411 which have come to be known as the Bentley Oxygenator. At the present time, such oxygenators are used more frequently than any other type. Among the important features of the oxygenators disclosed in the foregoing patents, the disclosures of which are incorporated herein by reference, was the provision of a self-contained heat exchanger.
In the intervening years, some relatively minor modifications have been made in bubble oxygenators, e.g., those disclosed in Brumfield U.S. Pat. Nos. 3,764,271 and 3,769,162. However, all rigid bubble oxygenators shown in the aforesaid patents and all other such oxygenators known to applicant to have been put to actual clinical use have had one fundamental feature in common, namely, each of them introduced blood and oxygen-rich gas in the lower region of the device and caused a column of bubbles to flow upwardly through the initial portion of the device. Bentley, et. al. U.S. Pat. Nos. 3,488,158 and 3,578,411 and the aforesaid Brumfield Patents do have some downward portions in the flow path of the gas blood mixture, but it is clear that they were designed to provide for initial upward flow of the gas and blood mixture in that portion of the flow path where the bubbles are formed. In addition, Fields U.S. Pat. No. 3,204,631, discloses an oxygenator in which blood enters at an upper portion and oxygen enters at a lower portion such that there is a counterflow relationship with the blood initially flowing downwardly and the oxygen flowing upwardly.